1. Field of the Invention
This invention relates to cathode ray tubes and more particularly, to so-called laminated implosion protection cathode ray tubes in which a safety panel is bonded to the face plate of the tube through a specific type of resin composition.
2. Description of the Prior Art
High resolution picture tubes are now used as video display terminals. As such tubes, there are ordinarily used laminated implosion protection cathode ray tubes in which a tempered safety panel is bonded to the front face of the face plate through adhesive resins. With high quality tubes, an anti-reflective film is further provided on the surface of the safety panel in order to mitigate the fatigue of users. The anti-reflective film can reduce a reflection factor on the safety panel surface by 4%, as compared with the case where no anti-reflective film is used, thus making it easier to watch the screen. With this type of cathode ray tube, it is usual for users to watch the screen at a close range of about 30 cm and thus the screen should desirably be free of any defects. For adhesive resins, there are ordinarily used polyester resins. The polyester resins are inexpensive and have good transparency, weatherability and flexibility, so that they are suitable for use as an interlayer resin. Since any resins which are transparent and flexible may be used as the adhesive resin, epoxy resins and silicone resins are usable for these purposes.
The defects on the screen may be derived from the safety panel, face plate, anti-reflective film, and resin.
When unsaturated polyester resins are used as adhesive resins in the laminated implosion protection cathode ray tube, there are produced, upon curing of the adhesive resin, fine particles of foreign matter whose refractive index is slightly different from the refractive index of the resin. These particles of foreign matter result in heterogeneous defects, or so-called glittering point defects. This glittering point phenomenon does not appear pronounced for domestic cathode ray tubes where the pitches of dots or stripes, or scanning lines on the fluorescent screen are coarse e.g. pitches of dots or stripes exceed 0.5 mm. However, the phenomenon becomes undesirably conspicuous for high resolution picture tubes where pitches of dots and stripes are below 0.4 mm.